1901] VEGETATION IN WESTERN TEXAS 2Qg1 
6. Annuals whose vegetation period covers only a few weeks 
exist generally in pure formation in all parts of the region hav- 
ing a constant annual recurrence of temperature and moisture 
conditions suited to the species in question. Thus the plains 
from the lower Rio Grande to the Red river and northward may 
possess successively the same ephemeral but extremely brilliant 
formations., 
7. The vegetation native to the region before the coming of 
civilization is undergoing profound changes as a result of dis- 
turbed equilibrium. This is no doubt exterminating certain 
species, epecially grasses. The chief results of the changes 
appear in establishing a woody or weed vegetation, and in the 
denudation of the hill country. 
UNIVERSITY OF TEXAS, AUSTIN. 
